<html>
  <style>
    body {
      background: lightgrey;
    }

    .container {
      position: fixed;
      top: 100px;
      left: 100px;
      width: 100px;
      height: 100px;
      isolation: isolate;
    }

    .content {
      position: absolute;
      top: 0px;
      left: 0px;
      width: 100%;
      height: 100%;
    }

    .new {
      background-color: red;
    }

    .old {
      background-color: blue;
      mix-blend-mode: multiply;
    }

  </style>
<body>
  <div class="container">
    <div class="content new"></div>
    <div class="content old"></div>
  </div>
</body>
</html>
